Different processes are known which comprise at least one step of extrusion cooking a mixture of water and a dry premix mainly comprising cereal flour or semolina.
AU-A-4591389 (GERBER PRODUCTS COMPANY) discloses a process for producing instant cereals which comprises moistening a dry blend mainly comprising a cereal flour and including additional oil and vitamins, extrusion cooking the moistened blend into an expanded rope, slicing the rope into puffs, grinding and screening the puffs to give a fine powder-like particle size, and agglomerating the particles into granules.
EP-A-0524329 (SOCIETE DES PRODUITS NESTLE S.A.) discloses a process for the manufacture of precooked cereal foods by extrusion cooking a moist blend of cereals, wherein a compressed gas is injected into the blend at the end of the cooking stage, just before the extrusion stage.
Further, many uses of gear pumps are known, for example supplying well metered amounts of food materials into relatively complicated coextrusion apparatus.
EP-A-0202143 (NABISCO BRANDS INC.) discloses a triple coextruder capable of coaxially coextruding two cooking doughs having different compositions and textures separated by a layer of an oil-based material serving as a moisture barrier, the doughs and the oil-based material being metered into respective nozzle portions of the coextruder by gear pumps, for example.
EP-A-0280484 (KOBAYASHI, MASAO) discloses a coextrusion apparatus capable of forming a globular food product by wrapping a center material with one or more layers of other food materials, in which the different materials are also metered into respective nozzle portions of the coextrusion apparatus by gear pumps, for example.